Two-step recruitment of RNA-directed DNA methylation to tandem repeats.
Two-step recruitment of RNA-directed DNA methylation to tandem repeats.
复制标题
将RNA定向DNA甲基化的两步募集到串联重复序列。
DOI：
10.1371/journal.pbio.0040363
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发表时间：
2006-11
期刊：
影响因子：
9.8
通讯作者：
Jacobsen, Steven E
中科院分区：
文献类型：
--
作者：
Chan, Simon W-L;Zhang, Xiaoyu;Bernatavichute, Yana V;Jacobsen, Steven E
串联重复序列经常与基因沉默现象有关。拟南芥FWA基因含有两个串联重复序列，当它被转化到植物中时，它是RNA指导的从头DNA甲基化的有效靶点。我们证明了FWA串联重复序列对于从头DNA甲基化是必要的和充分的，重复特征而不是内在序列可能是重要的。内源FWA可以采用两种稳定的表观遗传状态之一：甲基化和沉默，或非甲基化和活跃。令人惊讶的是，我们在两个州都发现了与FWA相关的小干扰RNA(SiRNA)。尽管如此，只有内源性FWA的甲基化形式才能招募到进一步的RNA指导的DNA甲基化或导致转基因FWA的有效从头甲基化。这表明RNA指导的DNA甲基化发生在两个步骤：第一，siRNA产生机制的初始招募，第二，siRNA指导的DNA甲基化，无论是顺式还是反式。第二步的效率取决于产生siRNA的基因座的性质，在某些基因座上，它可能需要预先存在的染色质修饰，如DNA甲基化本身。通过预先存在的DNA甲基化增强RNA导向的DNA甲基化可以创建一个自我增强系统来增强沉默的稳定性。在整个拟南芥基因组中，串联重复产生siRNAs，这表明重复获取可能是基因沉默进化的一种一般机制。在拟南芥中，由FWA转基因介导的甲基化和沉默需要FWA上游的串联重复序列，并且不依赖于siRNA的结合。
Tandem repeat sequences are frequently associated with gene silencing phenomena. The Arabidopsis thaliana FWA gene contains two tandem repeats and is an efficient target for RNA-directed de novo DNA methylation when it is transformed into plants. We showed that the FWA tandem repeats are necessary and sufficient for de novo DNA methylation and that repeated character rather than intrinsic sequence is likely important. Endogenous FWA can adopt either of two stable epigenetic states: methylated and silenced or unmethylated and active. Surprisingly, we found small interfering RNAs (siRNAs) associated with FWA in both states. Despite this, only the methylated form of endogenous FWA could recruit further RNA-directed DNA methylation or cause efficient de novo methylation of transgenic FWA. This suggests that RNA-directed DNA methylation occurs in two steps: first, the initial recruitment of the siRNA-producing machinery, and second, siRNA-directed DNA methylation either in cis or in trans. The efficiency of this second step varies depending on the nature of the siRNA-producing locus, and at some loci, it may require pre-existing chromatin modifications such as DNA methylation itself. Enhancement of RNA-directed DNA methylation by pre-existing DNA methylation could create a self-reinforcing system to enhance the stability of silencing. Tandem repeats throughout the Arabidopsis genome produce siRNAs, suggesting that repeat acquisition may be a general mechanism for the evolution of gene silencing. InArabidopsis, methylation and silencing mediated by theFWA transgene are found to require the tandem repeat sequences upstream ofFWA and to be independent of siRNA association.